This invention relates generally to optical information processing and, in particular, to an integrated electro-optical cross-bar apparatus for performing parallel optical logic and arithmetic operations.
There is a fundamental difference between optical circuits, in which the information carriers are photons, and electronic circuits, where the carriers are electrons. In the former case the carriers do not interact with each other, while in the latter they do. This means that in optical devices there exist interconnect possibilities that do not exist with electronic hardware, in particular, interconnected parallel architectures which permit digital arithmetic and logic operations to be performed in a completely parallel, single step process. After the inputs are switched on, the output appears in the time it takes a photon to transit the device. No faster computation time is possible.
Several recent patent applications have described techniques for optically performing logic and residue arithmetic in a single logical step. These applications include co-pending application Ser. No. 019,761 filed Feb. 27, 1987 by Falk et al, pending, and co-pending application Ser. No. 219,276 filed July 15, 1988, now U.S. Pat. No. 4,939,682, by Falk et al, both applications are incorporated herein by reference. The final logical step described therein was a parallel set of threshold logic devices. For the cross-bar structure, the threshold devices distinguish between light intensity levels of the 0 or 1 units and a light intensity level of 2 units. The threshold device essentially performs an AND function.
Ser. No. 019,761 describes an optical cross-bar arithmetic/logic unit that performs the above mentioned single step process by employing residue arithmetic. Residue arithmetic does not have a "carry" operation; that is, each "bit" in the representation is independent of the other. In residue arithmetic, each "bit" in a representation of a number is the decimal value of the number modulo the prime number corresponding to that position, called the "modulus" or the "radix".
The optical cross-bar arithmetic/logic disclosed in the above mentioned co-pending application utilizes cross optical paths of light which are configured to define intersecting regions with each other corresponding to truth table or logic table inputs. The intensity of light at each intersecting region is directed to determine if 2 units of light intensity are present at each intersection, thereby indicating a particular logic state.
In co-pending application Ser. No. 219,276, filed July 15, 1988 by R. Aaron Falk, there is disclosed a device to maximizing the performance and reducing the size of the optical cross-bar arithmetic/logic unit by forming the wave guide and electronic detectors of an optical cross-bar arithmetic/logic unit together in a single integrated electro-optic chip.